1. Field of the Invention
This application relates generally to apparatus for supporting a complex part such as a stamped sheet metal inner door panel having compound curves in a fixed position for surface measurements without interference to measurement by clamps or fixtures which project from the surface. Basically, the subject apparatus provides a substantially clampless support arrangement to accurately secure a complex part for measurement by automatically controlled digital measuring equipment.
2. Background of the Invention
For monitoring stamping quality, the surface of a relatively complex automobile body part such as a vehicle inner door panel is digitally measured through digital electronic automation (DEA). The DEA process utilizes an automatic tracking device or coordinate measuring machine (CCM) to move an sensor in relation to a stamped part to be measured. The sensor is mounted upon an arm and is selectively moved to contact particular sites on a surface of the stamped part to generate digital measurement data. This digital data is received into a computer which is programmed to compare the measurements with a set of desired geometric dimensions and tolerances (GD & T).
It is important that a vehicle inner door panel is accurately produced as a vehicle door is a composite of at least an inner and an outer panel to produce the complete vehicle door. The outer panel is attached to the inner panel and how well the door fits in an opening in the vehicle body can be effected by the accuracy of the inner and outer door panels. Thus, both panels must be assembled and attached together in a manner to create a very accurate composite. Both the inner and the outer panel have a relatively complex shape with non-parallel curved surfaces. If the panels are inaccurately formed during the stamping operation, the resultant composite door may not accurately fit in the vehicle door opening or its exterior surface may not properly align with the adjacent surfaces of the other parts of the vehicle.
Currently, deviations from desired GD & T are uncovered by periodically measuring a sample door panel by the CMM. As previously mentioned, the CMM supports a surface measuring sensor, essentially a very accurate switch. Such a sensor which is currently used to measure surfaces is manufactured by Renishaw in the United Kingdom, Model K60606. As the CMM moves the sensor, it measures various selected surface sites on the stamped part and feeds the data into the associated computer in digital format. The computer is programmed to receive the data and compare it with the GD & T to determine whether the part is within desired specifications and tolerances.
However, before measurements can be taken and data generated, the sample stamped part must first be accurately positioned in a desired orientation and then accurately held in that position during the measurement process. Thus, before using the CMM to take measurement data, a plurality of adjustable support columns (usually four or five) are very accurately positioned. The support columns support the stamped part to be measured which is laid over the support columns. When the columns are properly adjusted in a vertical direction, the stamped part is rigidly supported but must be restrained against the upper ends of the columns to prevent movements. Currently, clamps are used to hold a stamped part against the upper end of the columns. A typical clamp has a U-shaped configuration allowing it to extend around the edge portion of the stamped part. This unfortunately also places a portion of the clamp over a portion of the surface to be measured with a portion projecting upwardly from the surface. This upwardly projecting portion of the clamp usually will interfere with the movement of the sensor. In fact, measurements adjacent the clamp are usually impossible without first reclamping the part away from the desired measurement area and then removing that clamp that interferes with the desired measurement. In addition, unless very carefully regulated, an excess force can be placed on the stamped part by the clamp which can cause distortion of the part and resultant inaccuracies in surface measurement.